ISDN switching systems are deployed around the world, making new features and services available to customers. According to ISDN standards as set forth by the International Telegraph and Telephone Consultative Committee (CCITT), ISDN CPEs communicate with ISDN switching systems in two 64 kilobits per second (kbps) channels, referred to as B-channels, and in one 16 kbps channel referred to as a D-channel. Each of the B-channels is usable to convey digitized voice samples at the rate of 8,000 8-bit samples per second or data at a rate of 64 kbps. The D-channel is used both to convey signaling packets to effect message signaling between ISDN stations and switches or other ISDN stations and to convey data packets among ISDN stations. ISDN provides end-to-end digital connectivity to transmit voice, audio, visual and data information through a limited set of service independent user-network interfaces.
The interfaces for transmission between ISDN CPEs and an ISDN line to a switching system is a digital subscriber line (DSL). One such interface is a 4-wire DSL that conveys a serial bit stream at the rate of 192 kbps, which comprises 144 kbps, for the above-mentioned two 64 kbps B-channels and one 16 kbps D-channel and an additional 48 kbps used for a number of functions including framing, DC balancing, control and maintenance. A 4-wire DSL is referred to by the CCITT as the T interface. CCITT recommendations also recognize a U interface, which provides ISDN service using a 2-wire DSL. This 2-wire DSL transmits a serial bit stream at the rate of 80 K signals per second where each signal conveys four levels of information (2 bits), yielding an effective data rate of 160 kbps, thus providing two 64 kbps B-channels, one 16 kbps D-channel, and 16 kbps for signaling and maintenance information. Both the T and U interfaces include a further pair of wires for powering the CPE. As will be appreciated, a typical ISDN telephone requires a minimum of 34 V DC to operate.
While the U and T interfaces are constructed and operate differently, both interfaces can be found on customer premises for connection directly to the CPE. Because different data bit streams are transmitted over different lines and at different rates for the two interfaces, a CPE will only function if the CPE interface is compatible with the network interface. Thus, if a T interface CPE is connected to a U interface on the network the CPE will not operate. The reverse is also true.
A U to T converter, known as an NT1, has been developed that converts a U interface network to a T interface such that a T interface CPE can be used with the U interface network. A problem with the NT1 is that the user must know whether the network interface is a T or a U and whether the CPE interface is a T or U. It is only after this diagnosis is made that the user will be able to use the U to T converter. Moreover, to insure that any CPE is usable at any ISDN interface, the user must have a separate converter available at each network interface.
Further, while the design of both the U and T interfaces are now standardized, non-standard U interfaces were designed as a result of CCITT recommendations that allowed the local service provider to develop its own U interface design (the standard T interface was limited to a single mandatory design with the expectation that it would provide a standard interface for premises equipment manufacturers). In the United States, where a number of independent carriers provide local service in different geographic areas, different service providers developed and used different U interface designs until 1990 when the standardized 2B1Q was adopted by American National Standards Institute (ANSI). Although this standard U interface was adopted in 1990, existing non-standardized U interfaces remain in use. Because these non-standard network interfaces deliver power and/or signals on different lines than the standard ISDN interfaces, standard ISDN CPEs will not operate with these interfaces. Moreover, because power is delivered on different leads, it is possible to damage a standard ISDN CPE by connecting it to a non-standard U network interface.
In addition to ISDN systems, traditional analog telephone systems are widely used. Network interfaces for analog lines consist of a single pair of wires (tip and ring) for transmitting both signals and power to the telephone station set. Thus, unlike ISDN interfaces, network interfaces for analog lines do not include a separate pair of wires for transmitting power to the CPE. The typical analog telephone requires 48 V DC to operate.
Therefore, a problem in the art exists in that because of various network interfaces, the installation and relocation of CPE equipment requires significant user knowledge and diagnostics.